A Microelectromechanical Systems (MEMS) device, such as a MEMS device used in a gyroscope or an accelerometer, is typically sensitive to thermal and mechanical stresses. In the prior art, the MEMS device is directly mounted to the floor or substrate of a ceramic chip carrier package. The MEMS device typically is manufactured from silicon. The material from which the package is manufactured typically does not provide a good match with the material of the MEMS device in terms of their respective coefficients of thermal expansion. Furthermore, the MEMS device typically is bonded to the package by brazing. The braze materials may impart similar thermal stress to the MEMS device.
One type of prior art device uses an interposer to isolate the MEMS device from the package. The interposer is a device upon which a MEMS device is mounted. The interposer is in turn mounted in the MEMS package. The function of the interposer is to isolate the MEMS device from the mechanical and thermal stress exerted by the package. FIG. 1 illustrates a schematic structure of the package, the interposer, and the MEMS device. The MEMS device and the interposer are manufactured as two separate entities. The MEMS device is subsequently brazed to the interposer using a gold and/or tin alloy. One disadvantage of the prior art structure is that the braze materials may impart thermal stresses to the MEMS device. Furthermore, the braze materials may creep over time. This negatively affects the long term performance stability and reliability of the MEMS device.
Moreover, in the prior art device, the MEMS device typically includes a substrate and a silicon device attached to the substrate. The substrate is bonded to the interposer by brazing. The substrate is manufactured from glass or other materials. In the situation that the substrate is not manufactured from the same material as the silicon device, the substrate may also impart thermal stresses to the silicon device. This may degrade the performance of the whole system.
FIG. 2 illustrates a traditional method of producing the MEMS device, in which the interposer and the MEMS device are manufacture as two separate entities. The process starts from the top of the figure and continues to the bottom of the figure. The traditional process of making an interposer starts with a double-side polished silicon wafer 10. Oxide layers 12 are grown on both sides of the silicon wafer 10. On a top side of the wafer 10, the oxide layer is selectively etched, and ohmic contacts 14 and braze materials 16 are deposited in the etched area. The MEMS device as denoted by number 22 generally includes a silicon device 24 attached to a substrate 26. Typically, the silicon device 24 is attached to the substrate 26 by anodic bonding. The substrate 26 is then attached to the interposer 10 by brazing. The traditional materials used in brazing are gold and tin. The brazing materials between the substrate 26 and the interposer 10 may creep over time, and that may have negative effects on the performance of the MEMS device.
What is needed is a structure having a MEMS device and an interposer, wherein the interposer has a thermal expansion well-matched to the MEMS device. There is a further need of a method of manufacturing the structure.